Method And System For Explicit Feedback With Sounding Packet For Wireless Local Area Networks (WLAN)

ABSTRACT

Aspects of a method and system for explicit feedback with a sounding packet for wireless local area networks (WLAN). Aspects of the system may include a beamforming block that may enable generation of a plurality of RF chain signals based on a current steering matrix, where the current steering matrix may be a non-identity matrix. A processor may enable transmission of a request for feedback information via the plurality of RF chain signals. The request may contain medium access control (MAC) layer protocol data unit (PDU) data and channel sounding information, which may be encapsulated in a physical (PHY) layer PDU.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation of U.S. Utility application Ser. No.11/535,794, entitled “Method and System for Explicit Feedback withSounding Packet for Wireless Local Area Networks (WLAN),” filed Sep. 27,2006, pending, which claims priority pursuant to 35 U.S.C. §119(e) toU.S. Provisional Application Ser. No. 60/830,928, entitled “Method andSystem for Explicit Feedback with Sounding Packet for WLAN,” filed Jul.14, 2006, now expired, both of which are incorporated herein byreference for all purposes.

This application makes reference to:

-   U.S. patent application Ser. No. 11/450,818 filed on Jun. 9, 2006;-   U.S. patent application Ser. No. 11/327,752 filed on Jan. 6, 2006;-   U.S. patent application Ser. No. 11/393,224 filed on Mar. 30, 2006;    and-   U.S. application Ser. No. 11/110,241 filed Apr. 20, 2005.

Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for quantization for explicit feedback with a soundingpacket for WLAN.

BACKGROUND OF THE INVENTION

Multiple input multiple output (MIMO) systems are wirelesscommunications systems that may transmit signals utilizing a pluralityof transmitting antennas, and/or receive signals utilizing a pluralityof receiving antennas. Communications between MIMO systems may be basedon specifications from the Institute of Electrical and ElectronicsEngineers (IEEE). A MIMO system that receives a signal Y may compute achannel estimate matrix, H, based on the received signal. The signal maycomprise information generated from a plurality of information sources.Each such information source may be referred to as a spatial stream. Atransmitting MIMO system may utilize a plurality of transmittingantennas when transmitting a corresponding signal X. A receiving MIMOsystem may utilize a plurality of receiving antennas when receiving thesignal Y. The channel estimate matrix for a downlink RF channel,H_(down), may describe a characteristic of the wireless transmissionmedium in the transmission path from a transmitter, to a receiver. Thechannel estimate for an uplink RF channel, R_(up), may describe acharacteristic of the wireless transmission medium in the transmissionpath from the receiver to the transmitter.

According to the principle of reciprocity, a characteristic of thewireless transmission medium in the transmission path from thetransmitter to the receiver may be assumed to be identical to acorresponding characteristic of the wireless transmission medium in thetransmission path from the receiver to the transmitter. However, thechannel estimate matrix H_(down) may not be equal to a correspondingchannel estimate matrix for an uplink RF channel R_(up). For example, anoise level, for example an ambient noise level, in the vicinity of thetransmitter may differ from a noise level in the vicinity of thereceiver. Similarly, an interference level, for example electro-magneticinterference due to other electro-magnetic devices, in the vicinity ofthe transmitter may differ from an interference level in the vicinity ofthe receiver. At a transmitter, or receiver, there may also beelectrical cross-coupling, for example leakage currents, betweencircuitry associated with a receiving antenna, or a transmittingantenna, and circuitry associated with another receiving antenna, oranother transmitting antenna.

The principle of reciprocity, wherein it may be assumed thatH_(up)=H_(down), may also be based on the assumption that specificantennas at a transmitter or receiver are assigned for use astransmitting antennas, and/or assigned for use as receiving antennas. Atthe transmitter, a number of receiving antennas, N_(RX), utilized at thereceiver may be assumed. At the receiver, a number of transmittingantennas, N_(TX), utilized at the transmitter may be assumed. If theassignments of at least a portion of the antennas at the transmitter arechanged, the corresponding channel estimate matrix H′_(up) may not beequal H_(down). Similarly, if the assignments of at least a portion ofthe antennas at the receiver are changed, the corresponding channelestimate matrix H′_(down) may not be equal R_(up). Consequently, afterreassignment of antennas at the transmitter and/or receiver, theprinciple of reciprocity may not be utilized to characterizecommunications between the transmitter and the receiver when H_(up) doesnot equal H′_(down), when H′_(up) does not equal H_(down), or whenH′_(up) does not equal H′_(down).

The principle of reciprocity may enable a receiving wireless local areanetwork (WLAN) device A to receive a signal Y from a transmitting WLANdevice B, and to estimate a channel estimate matrix H_(down) for thetransmission path from the transmitting WLAN device B to the receivingWLAN device A. Based on the channel estimate matrix H_(down), the WLANdevice A may transmit a subsequent signal X, via an uplink RF channel,to the WLAN device B based on the assumption that the channel estimatematrix H_(up) for the transmission path from the transmitting WLANdevice A to the receiving WLAN device B may be characterized by therelationship H_(up)=H_(down). When the WLAN devices A and B are MIMOsystems, corresponding beamforming matrices may be configured andutilized for transmitting and/or receiving signals at each WLAN device.

Beamforming is a method for signal processing that may allow atransmitting MIMO system to combine a plurality of spatial streams in atransmitted signal X. Beamforming may comprise computing a matrix ofbeamforming coefficients. The beamforming coefficients may be utilizedto compute a plurality of weighted sums representing a correspondingcombination of signal strength levels from at least a portion of theplurality of spatial streams. Each weighted sum may be referred to as aradio frequency (RF) chain. A transmitting WLAN device maysimultaneously transmit an RF chain from each of the plurality oftransmitting antennas. The transmitted signal X may comprise theplurality of transmitted RF chains. Beamforming is also a method forsignal processing that may allow a receiving MMO system to separateindividual spatial streams in a received signal Y.

As a result of a failure of an assumed condition for the principle ofreciprocity, a beamforming matrix at the transmitting WLAN device,and/or an equalization matrix at the receiving WLAN device, may beconfigured incorrectly. In a transmitted signal X, from the perspectiveof a signal associated with an i^(th) spatial stream, a signalassociated with a j^(th) spatial stream may represent interference ornoise. Incorrect configuration of one or more beamforming matrices mayreduce the ability of the receiving WLAN device to cancel interferencebetween an i^(th) spatial stream and a j^(th) spatial stream.Consequently, the received signal Y may be characterized by reducedsignal to noise ratios (SNR). There may also be an elevated packet errorrate (PER) when the receiving WLAN device decodes information containedin the received signal Y. This may, in turn, result in a reducedinformation transfer rate, as measured in bits/second, forcommunications between the transmitting WLAN device and the receivingWLAN device.

In some MIMO systems, a transmitting WLAN device may transmit aplurality of spatial streams based on channel state information at thetransmitter (CSIT). The CSIT may be based on feedback information sentfrom the receiving WLAN device B to the transmitting WLAN device A.Based on the CSIT, the transmitting WLAN device A may compute estimatedvalues for the channel estimate matrix H_(down).

Channel sounding is one method by which a transmitting WLAN device mayreceive CSIT from a receiving WLAN device. When performing a channelsounding procedure, the transmitting WLAN device may transmit one ormore sounding frames to the receiving WLAN device. In some MIMO systems,the sounding frames may be transmitted without beamforming by aplurality of RF chains. In this respect, the matrix utilized forgenerating a plurality of RF chains from a plurality of spatial streamsmay comprise an identity matrix.

Upon receipt of a sounding frame, the receiving WLAN device may begin tocompute channel state information (CSI). The CSI may be represented bythe channel estimate matrix H. The CSI may be sent to the transmittingWLAN device as feedback information. The receiving WLAN device may notutilize beamforming when transmitting signals for sending the CSI to thetransmitting WLAN device. The transmitting WLAN device may utilize thereceived feedback information to generate a beamforming matrix. Thetransmitting WLAN device may utilize the beamforming matrix to transmitone or more subsequent frames comprising data in a subsequenttransmitted signal X. After receiving the subsequent frames, thereceiving WLAN device may send an acknowledgement frame to thetransmitting WLAN device. The receiving WLAN device may not utilizebeamforming when transmitting signals for sending the acknowledgementframe to the transmitting WLAN device.

In some MIMO systems, the channel sounding procedure comprises time oneor more time durations during which a plurality of RF chains may betransmitted without utilizing beamforming. During these periods, atransmitting WLAN device may not be able to transmit data from one ormore spatial streams in a transmitted signal X, such that the receivingWLAN device would be able to generate estimates for each of the spatialstreams in a received signal Y. In this regard, the amount of timerequired to perform the channel sounding procedure may result in areduction in the information transfer rate between the transmitting WLANdevice and the receiving WLAN device.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for explicit feedback with a sounding packet forWLAN, substantially as shown in and/or described in connection with atleast one of the figures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary system for wireless datacommunications, which may be utilized in connection with an embodimentof the invention.

FIG. 2 is a block diagram of an exemplary wireless transceiver systemthat may be utilized in connection with an embodiment of the invention.

FIG. 3 is an exemplary diagram illustrating channel feedback, which maybe utilized in connection with an embodiment of the invention.

FIG. 4 is an exemplary diagram illustrating beamforming that may beutilized in connection with an embodiment of the invention.

FIG. 5 is an exemplary block diagram of a MIMO transmitter, which may beutilized in connection with an embodiment of the invention.

FIG. 6 is a diagram that illustrates exemplary frame exchange in aconventional channel sounding procedure, which may be utilized inconnection with an embodiment of the invention.

FIG. 7 is a diagram that illustrates exemplary frame exchange utilizinga non-identity steering matrix in a channel sounding procedure, inaccordance with an embodiment of the invention.

FIG. 8 is a diagram that illustrates exemplary frame exchange fortransmitting data within channel sounding frames, in accordance with anembodiment of the invention.

FIG. 9 is a diagram illustrating an exemplary signal header field, whichmay be utilized in connection with an embodiment of the invention.

FIG. 10 is a flowchart illustrating exemplary steps for exemplary frameexchange for transmitting data within channel sounding frames, inaccordance with an embodiment of the invention.

FIG. 11 is a flowchart illustrating exemplary steps for exemplary frameexchange for transmitting channel sounding frames utilizing anon-identity steering matrix, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention relate to a method and system forexplicit feedback with a sounding packet for WLAN. In one exemplaryembodiment of the invention, beamforming may be utilized by atransmitting WLAN device for transmitting a sounding frame thatcomprises data from a plurality of spatial streams. Thus, thetransmitting WLAN device may initiate a channel sounding procedure whilecontinuing to transmit data, via beamformed RF chains, utilizing acurrent steering matrix that is not an identity matrix. In this regard,the sounding frame may be “piggybacked” on a data frame transmitted viaone or more beamformed RF chains. Based on feedback information receivedfrom the receiving WLAN device, the transmitting WLAN device maygenerate a subsequent steering matrix. The subsequent steering matrixmay be utilized for transmitting subsequent data via a subsequentplurality of RF chains. In this exemplary embodiment of the invention,the amount of time required to perform a channel sounding procedure maybe reduced, in comparison to conventional channel sounding proceduremethods.

In another exemplary embodiment of the invention, a channel soundingprocedure may be initialized by transmitting a sounding frame via aplurality of RF chains while utilizing a steering matrix that is not anidentity matrix. Based on feedback information received from thereceiving WLAN device, the transmitting WLAN device may generate asubsequent steering matrix. The subsequent steering matrix may beutilized for transmitting a subsequent frame comprising data via asubsequent plurality of RF chains. After receipt of the subsequent framethe receiving WLAN device may send an acknowledgement frame to thetransmitting WLAN device.

FIG. 1 is a block diagram of an exemplary system for wireless datacommunications, which may be utilized in connection with an embodimentof the invention. With reference to FIG. 1, there is shown adistribution system (DS) 110, an extended service set (ESS) 120, and anIEEE 802 LAN or WAN 122. The ESS 120 may comprise a first basic serviceset (BSS) 102, and a second BSS 112. The first BSS 102 may comprise afirst 802.11 WLAN station 104, a second 802.11 WLAN station 106, and anaccess point (AP) 108. The second BSS 112 may comprise a first 802.11WLAN station 114, a second 802.11 WLAN station 116, and an access point(AP) 118. The IEEE 802 LAN 122 or WAN may comprise a LAN or WAN station124, and a portal 126. An IEEE 802.11 WLAN station, or IEEE 802.11 WLANdevice, is a WLAN system that may be compliant with at least a portionof the IEEE 802.11 standard.

A WLAN is a communications networking environment that comprises aplurality of WLAN devices that may communicate wirelessly via one ormore uplink and/or downlink RF channels. The BSS 102 or 112 may be partof an IEEE 802.11 WLAN that comprises at least 2 IEEE 802.11 WLANstations, for example, the first 802.11 WLAN station 104, the second802.11 WLAN station 106, and the AP 108, which may be members of the BSS102. Non-AP stations within BSS 102, the first 802.11 WLAN station 104,and the second 802.11 WLAN station 106, may individually form anassociation with the AP 108. An AP, such as AP 108, may be implementedas an Ethernet switch, bridge, or other device in a WLAN, for example.Similarly, non-AP stations within BSS 112, the first 802.11 WLAN station114, and the second 802.11 WLAN station 116, may individually form anassociation with the AP 118. Once an association has been formed betweena first 802.11 WLAN station 104 and an AP 108, the AP 108 maycommunicate reachability information about the first 802.11 WLAN station104 to other APs associated with the ESS 120, such as AP 118, andportals such as the portal 126. The WLAN station 104 may subsequentlycommunicate information wirelessly via the BSS 102. In turn, the AP 118may communicate reachability information about the first 802.11 WLANstation 104 to stations in BSS 112. The portal 126, which may beimplemented as, for example, an Ethernet switch or other device in aLAN, may communicate reachability information about the first 802.11WLAN station 104 to stations in LAN or WAN 122 such as the 802 LAN orWAN station 124. The communication of reachability information about thefirst 802.11 WLAN station 104 may enable WLAN stations that are not inBSS 102, but are associated with ESS 120, to communicate wirelessly withthe first 802.11 WLAN station 104 through ESS 120.

The DS 110 may provide an infrastructure which enables a first 802.11WLAN station 104 in one BSS 102, to communicate wirelessly with a first802.11 WLAN station 114 in another BSS 112. The DS 110 may also enable afirst 802.11 WLAN station 104 in one BSS 102 to communicate with an 802LAN or WAN station 124 in an IEEE 802 LAN or WAN 122, implemented as,for example a wired LAN or WAN. The AP 108, AP 118, or portal 126 mayprovide a means by which a station in a BSS 102, BSS 112, or LAN or WAN122 may communicate information via the DS 110. The first 802.11 WLANstation 104 in BSS 102 may communicate information wirelessly to a first802.11 WLAN station 114 in BSS 112 by transmitting the informationwirelessly to AP 108, which may transmit the information via the DS 110to AP 118, which in turn may transmit the information wirelessly tostation 114 in BSS 112. The first 802.11 WLAN station 104 maycommunicate information wirelessly to the 802 LAN or WAN station 124 inLAN or WAN 122 by transmitting the information wirelessly to AP 108,which may transmit the information via the DS 110 to the portal 126,which in turn may transmit the information to the 802 LAN or WAN station124 in LAN or WAN 122. The DS 110 may utilize wireless communicationsvia an RF channel, wired communications, such as IEEE 802.3 or Ethernet,or a combination thereof.

A WLAN station, such as 104, 114, or AP, such as 108, 118, may utilizeone or more transmitting antennas, and one or more receiving antennaswhen communicating information. A WLAN station or AP that utilizes aplurality of transmitting antennas and/or a plurality of receivingantennas may be referred to as a multiple input multiple output (MIMO)system.

FIG. 2 is a block diagram of an exemplary wireless transceiver systemthat may be utilized in connection with an embodiment of the invention.The wireless transceiver may be utilized in connection with a portal126, an access point 106, and/or an 802.11 WLAN station 104, forexample. An exemplary embodiment of a transceiver may be a wirelessnetwork interface subsystem. With reference to FIG. 2 there is shown atransceiver 274, an RF front end 280, one or more receiving antennas 276a, . . . , 276 n, and one or more transmitting antennas 278 a, . . . ,278 n. The transceiver 274 may comprise a processor 282, memory 272, areceiver 284, and a transmitter 286.

The processor 282 may perform digital receiver and/or transmitterfunctions in accordance with applicable communications standards. Thesefunctions may comprise, but are not limited to, tasks performed at lowerlayers in a relevant protocol reference model. These tasks may furthercomprise the physical layer convergence procedure (PLCP), physicalmedium dependent (PMD) functions, and associated layer managementfunctions. These tasks may further comprise medium access control (MAC)layer functions as specified by pertinent standards.

The memory 272 may comprise suitable logic, circuitry, and/or code thatmay be utilized to enable storage and/or retrieval of data and/or code.Stored code may, for example, comprise an implementation for a bridgingand/or routing protocol. Stored data may, for example, comprise datacompiled based on execution of code for a routing and/or bridgingprotocol. Stored data may also comprise received data, and/or data to betransmitted. Retrieved data and/or code may be assigned physicalresources within the memory 272 for the storage. The stored data and/orcode may be subsequently available for retrieval. Retrieved data and/orcode may be output by the memory 272 and communicated to other devices,components, and/or subsystems that may be communicatively coupled,directly and/or indirectly, to the memory 272. The memory 272 may enablethe stored data and/or code to remain stored and/or available forsubsequent retrieval until the resources allocated for the storage aredeallocated. Physical resources may be deallocated based on a receivedinstruction that the stored data and/or code be erased from the memory272, or based on a received instruction that the physical resources beallocated for the storage of subsequent data and/or code. The memory mayutilize a plurality of storage medium technologies such as volatilememory, for example, random access memory (RAM), and/or nonvolatilememory, for example, electrically erasable programmable read only memory(EEPROM).

The receiver 284 may perform digital receiver functions that maycomprise, but are not limited to, fast Fourier transform processing,beamforming processing, equalization, demapping, demodulation control,deinterleaving, depuncture, and decoding. The transmitter 286 mayperform digital transmitter functions that comprise, but are not limitedto, coding, puncture, interleaving, mapping, modulation control, inversefast Fourier transform processing, beamforming processing. The RF frontend 280 may receive analog RF signals via the one or more antennas 276a, . . . , 276 n, by converting the RF signal to baseband and generatinga digital equivalent of the received analog baseband signal. The RFfront end 280 may also transmit analog RF signals via an antenna 278 a,. . . , 278 n, by converting a digital baseband signal to an analog RFsignal.

In operation, the processor 282 may receive data from the receiver 284.The processor 282 may communicate received data to the memory 272 forstorage. The processor 282 may enable retrieval of data from the memory272 to be transmitted via an RF channel by the transmitter 286. Thememory 272 may communicate the data to the processor 282. The processor282 may generate signals to control the operation of the modulationprocess in the transmitter 286, and of the demodulation process in thereceiver 284.

FIG. 3 is an exemplary diagram illustrating channel feedback, which maybe utilized in connection with an embodiment of the invention. Referringto FIG. 3, there is shown a transmitting mobile terminal 302, areceiving mobile terminal 322, and a communications medium 344. Thecommunications medium 344 may represent a wireless communicationsmedium. The transmitting mobile terminal 302 may transmit a signalvector X to the receiving mobile terminal 322 via the communicationsmedium 344. The communications direction from the transmitting mobileterminal 302 to the receiving mobile terminal 322 may be referred to asa downlink direction. The signal vector X may comprise a plurality ofspatial streams simultaneously transmitted via one or more transmittingantennas. The signal vector X may be beamformed by the transmittingmobile terminal 302 based on a beamforming matrix V. The signal vector Xmay travel through the communications medium 344. The signal vector Xmay be altered while traveling through the communications medium 344.The transmission characteristics associated with the communicationsmedium 344 may be characterized by a transfer function H. The signalvector X may be altered based on the transfer function H. In thedownlink direction, the transfer function H may be referred to asH_(down). The altered signal vector X may be represented as the signalY. The receiving mobile terminal 322 may receive the signal Y. Thereceiving mobile terminal 322 may determine one or more valuesassociated with the transfer function H_(down) based on the signal Yreceived via the communications medium 344.

The receiving mobile terminal 322 may compute one or more valuesassociated with a matrix V based on the information related to thetransfer function H_(down). The receiving mobile terminal 322 maycommunicate information related to the matrix V to the transmittingmobile terminal 302 as feedback information. The feedback information(H_(down)) may represent feedback information based on the informationrelated to the transfer function H_(down). The receiving mobile terminal322 may communicate the feedback information (H_(down)) via atransmitted signal vector X_(f). The transmitted signal vector X_(f) maybe transmitted to the transmitting mobile terminal 302 via thecommunications medium 344. The signal vector X_(f) may be altered whiletraveling through the communications medium 344. The communicationsdirection from the receiving mobile terminal 322 to the transmittingmobile terminal 302 may be referred to as an uplink direction. Thesignal vector X_(f) may be altered based on the transfer function H. Inthe uplink direction, the transfer function H may be referred to asR_(up). The altered signal vector X_(f) may be represented as the signalY_(f). The transmitting mobile terminal 302 may receive the signalY_(f).

The transmitting mobile terminal 302 may determine one or more valuesassociated with the transfer function H_(up) based on the signal Y_(f)received via the communications medium 344. The transmitting mobileterminal 302 may utilize the received feedback information (H_(down)) tobeamform subsequent signal vectors X, which may be transmitted in thedownlink direction from the transmitting mobile terminal 302 to thereceiving mobile terminal 322.

FIG. 4 is an exemplary diagram illustrating beamforming that may beutilized in connection with an embodiment of the invention. Referring toFIG. 4, there is shown a transmitting mobile terminal 402, a receivingmobile terminal 406, and a wireless communication medium 404. Anexemplary transmitting mobile terminal 402 may be a AP 108. An exemplaryreceiving mobile terminal 406 may be an 802.11 WLAN station 104. Thetransmitting mobile terminal 402 may be a MIMO system. The receivingmobile terminal 406 may be a MIMO system. The transmitting mobileterminal 402 comprises a transmit spatial mapping matrix 408, aplurality of inverse fast Fourier transform (IFFT) blocks 410 a, 410 b,. . . , and 410 n, and a plurality of transmitting antennas 412 a, 412b, . . . , and 412 n. The receiving mobile terminal 406 comprises aspatial equalizer 422, a plurality of fast Fourier transform (FFT)blocks 422 a, 422 b, . . . , and 422 n, and a plurality of receivingantennas 426 a, 426 b, . . . , and 426 n.

The spatial mapping matrix 408 may comprise a steering matrix Q thatperforms computations on a plurality of spatial streams, where Nss is avariable representing the number of spatial streams, and generates aplurality of transmitted RF chains, wherein Ntx is a variablerepresenting the number of transmitted RF chains. The plurality ofspatial streams may comprise a first spatial stream, Stream₁, a secondspatial stream, Stream₂, an Nss^(th) spatial stream, Stream_(Nss). Theplurality of transmitted RF chains may comprise a first transmitted RFchain, Tx Chain₁, a second transmitted RF chain, Tx Chain₂ 308, anNtx^(th) transmitted RF chain, Tx Chain_(Ntx). Each of the transmittedRF chains Tx Chain₁, Tx Chain₂, . . . , and Tx Chain_(Ntx), may comprisea corresponding weighted sum computed from the plurality of spatialstreams Stream₁, Stream₂, . . . , and Stream_(Nss), based oncoefficients in the steering matrix Q.

The IFFT block 410 a may perform IFFT calculations to transform afrequency-domain representation of the transmitted RF chain, Tx Chain₁,to a time-domain representation. The time-domain representation of thetransmitted RF chain, x₁, may be transmitted via the transmittingantenna 412 a to the wireless communications medium 404. The IFFT block410 b may perform IFFT calculations to transform a frequency-domainrepresentation of the transmitted RF chain, Tx Chain₂, to a time-domainrepresentation. The time-domain representation of the transmitted RFchain, x₂, may be transmitted via the transmitting antenna 412 b to thewireless communications medium 404. The IFFT block 410 n may performIFFT calculations to transform a frequency-domain representation of thetransmitted RF chain, Tx Chain_(Ntx), to a time-domain representation.The time-domain representation of the transmitted RF chain, x_(Ntx), maybe transmitted via the transmitting antenna 412 n to the wirelesscommunications medium 404. The plurality of simultaneously transmittedRF chains may be represented by a transmitted signal vector X.

The receiving antenna 426 a may receive a signal y₁ via the wirelesscommunications medium 404. The FFT block 424 a may perform FFTcalculations to transform a time-domain of the received signal, y₁, to afrequency-domain representation of a received RF chain, Rx Chain₁. Thereceiving antenna 426 b may receive a signal y₂ via the wirelesscommunications medium 404. The FFT block 424 b may perform FFTcalculations to transform a time-domain of the received signal, y₂, to afrequency-domain representation of a received RF chain, Rx Chain₂. Thereceiving antenna 426 n may receive a signal y_(Nrx) via the wirelesscommunications medium 404. Nrx may be a variable representing the numberof receiving antennas at the receiving mobile terminal 406. The FFTblock 424 n may perform FFT calculations to transform a time-domain ofthe received signal, y_(Nrx), to a frequency domain representation of areceived RF chain, Rx Chain_(Nrx). The plurality of received RF chainsmay be represented by a received signal vector Y.

The spatial equalizer 422 may comprise an equalization matrix U thatperforms computations on a received plurality of Nrx RF chains, andgenerates a plurality of Nss estimated spatial streams. The plurality ofreceived RF chains may comprise a first received RF chain, Rx Chain₁, asecond received RF chain, Rx Chain₂ 308, an Ntx^(th) received RF chain,Rx Chain_(Ntx). The plurality of estimated spatial streams may comprisea first estimated spatial stream, Ŝtream₁, a second estimated spatialstream, Ŝtream₂, and an Nss^(th) estimated spatial stream, Ŝtream_(Nss).Each of the plurality of estimated spatial streams at the receivingmobile terminal 406 may comprise an estimated value for a correspondingspatial stream at the transmitting mobile terminal 402.

Various embodiments of the invention may be practiced when the pluralityof spatial streams Stream₁, Stream₂, . . . , and Stream_(Nss) isreplaced by a plurality of space time streams STStream₁, STStream₂, . .. , and STStream_(Nsts), which may be generated based on space timecoding (STC) and/or space time block coding (STBC), where Nsts may be avariable that represents the number of space time streams. The pluralityof Nsts space time streams may be generated based on the plurality ofNss spatial streams.

The plurality of spatial streams at the transmitting mobile terminal402, Stream₁, Stream₂, . . . , and Stream_(Nss), may be represented bystream vector G as represented in the following equation:

$\begin{matrix}{G = \begin{bmatrix}{Stream}_{1} \\{Stream}_{2} \\\vdots \\{Stream}_{Nss}\end{bmatrix}} & {{Equation}\mspace{14mu}\lbrack 1\rbrack}\end{matrix}$

The plurality of transmitted signal vector X may be represented as inthe following equation:

$\begin{matrix}{{X = \begin{bmatrix}{TxChain}_{1} \\{TxChain}_{2} \\\vdots \\{TxChain}_{Ntx}\end{bmatrix}}{{where}\text{:}}} & {{Equation}\mspace{14mu}\lbrack 2\rbrack} \\{X = {Q \cdot G}} & {{Equation}\mspace{14mu}\lbrack 3\rbrack}\end{matrix}$

where Q may represent the steering matrix utilized by the spatialmapping matrix block 408, which may be represented as in the followingequation:

$\begin{matrix}{Q = \begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1,{Nss}} \\w_{21} & w_{22} & \ldots & w_{2,{Nss}} \\\vdots & \vdots & \ddots & \vdots \\w_{{Ntx},1} & w_{{Ntx},2} & \ldots & w_{{Ntx},{Nss}}\end{bmatrix}} & {{Equation}\mspace{14mu}\lbrack 4\rbrack}\end{matrix}$

where each element, w, in the matrix of equation [4] may represent abeamforming coefficient.

The received signal vector Y may be represented as in the followingequation:

$\begin{matrix}{{Y = \begin{bmatrix}{RxChain}_{1} \\{RxChain}_{2} \\\vdots \\{RxChain}_{Nrx}\end{bmatrix}}{{where}\text{:}}} & {{Equation}\mspace{14mu}\lbrack 5\rbrack} \\{Y = {{H \cdot Q \cdot G} + N}} & {{Equation}\mspace{14mu}\lbrack 6\rbrack}\end{matrix}$

where N may represent noise that may exist in the wireless communicationmedium 404, and H may represent the channel estimate matrix, which maybe represented as in the following equation:

$\begin{matrix}{H = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1,{Ntx}} \\h_{21} & h_{22} & \ldots & h_{2,{Ntx}} \\\vdots & \vdots & \ddots & \vdots \\h_{{Nrx},1} & h_{{Nrx},2} & \ldots & h_{{Nrx},{Ntx}}\end{bmatrix}} & {{Equation}\mspace{14mu}\lbrack 7\rbrack}\end{matrix}$

where each element, h, may describe channel fading properties of thewireless communications medium 404 for signals transmitted by atransmitting antenna at the transmitting mobile terminal 402, andreceived by a receiving antenna at the receiving mobile terminal 406. Asillustrated in FIG. 4, the channel estimate matrix H may be measuredfrom a point corresponding to the output of the spatial mapping matrix408, to a point corresponding to the input to the spatial equalizer 422.

The plurality of estimated spatial streams at the receiving mobileterminal 406, Ŝtream₁, Ŝtream₂, . . . , and Ŝtream_(Nss), may berepresented by stream vector Ĝ as in the following equation:

$\begin{matrix}{{\hat{G} = \begin{bmatrix}{\hat{S}{tream}_{1}} \\{\hat{S}{tream}_{2}} \\\vdots \\{\hat{S}{tream}_{Nss}}\end{bmatrix}}{{where}\text{:}}} & {{Equation}\mspace{14mu}\lbrack 8\rbrack} \\{{\hat{G} = {{U^{*} \cdot H \cdot Q \cdot G} + {U^{*} \cdot N}}}{or}} & {{Equation}\mspace{14mu}\lbrack {9\; a} \rbrack} \\{{\hat{G} = {{U^{*} \cdot H_{eff} \cdot G} + {U^{*} \cdot N}}}{{where}\text{:}}} & {{Equation}\mspace{14mu}\lbrack {9\; b} \rbrack} \\{H_{eff} = {H \cdot Q}} & {{Equation}\mspace{14mu}\lbrack 10\rbrack}\end{matrix}$

where U* may represent an Hermitian transform of the equalization matrixU, which may be utilized by the spatial equalizer block 422 and may berepresented as in the following equation:

$\begin{matrix}{U^{*} = \begin{bmatrix}u_{11}^{*} & u_{12}^{*} & \ldots & u_{1,{Ntx}}^{*} \\u_{21}^{*} & u_{22}^{*} & \ldots & u_{2,{Ntx}}^{*} \\\vdots & \vdots & \ddots & \vdots \\u_{{Nss},1}^{*} & u_{{Nss},2}^{*} & \ldots & u_{{Nss},{Ntx}}^{*}\end{bmatrix}} & {{Equation}\mspace{14mu}\lbrack 11\rbrack}\end{matrix}$

where each element, u, in the matrix of equation [4] may represent anequalization coefficient.

The matrix H_(eff) may be represented as a matrix comprising Nrx rowsand Nss columns. Alternatively, the matrix H_(eff) may be described asan Nrx×Nss matrix. When the number of spatial streams Nss equals thenumber of transmitting antennas Ntx, the matrix H_(eff) may berepresented as an Nrx x Ntx matrix.

In an exemplary embodiment of the invention utilizing singular valuedecomposition (SVD), the matrix H_(eff) may be represented as in thefollowing equation:

H _(eff) =U·S·V*  Equation [12]

where U may represent an equalization matrix, S may represent a diagonalmatrix, and V* may represent an Hermitian transpose of a beamformingmatrix V.

In other exemplary embodiments of the invention, the matrix V may bedetermined based on the matrix H_(eff), such as when utilizing geometricmean decomposition (GMD), for example.

In conventional MIMO systems, the steering matrix utilized by thespatial mapping matrix block 408 within the transmitting mobile terminal402 may be computed based on feedback information received from thereceiving mobile terminal 406. The receiving mobile terminal 406 maycompute the matrix V from equation [12] based on measured CSI derivedfrom the received signal vector Y, which may be utilized to compute thematrix H_(eff), and on the equalization matrix U, utilized by thespatial equalizer block 422. The matrix Q may be an identity matrix. Thematrix V may be sent from the receiving mobile terminal 406 to thetransmitting mobile terminal 402 in the feedback information. The matrixV may be represented as an Ntx×Nss matrix.

The transmitting mobile terminal 402 may utilize the matrix V receivedin feedback information as a subsequent steering matrix that is utilizedfor transmitting a subsequent transmitted signal vector X. In this case:

Ĝ=U*·H·V·G+U*·N  Equation [13]

Based on equations [10] and [12]:

H·Q=U·S·V*  Equation [14a]

and

H·Q·Q*=U·S·V*·Q*  Equation [14b]

H=U·S·V*·Q*  Equation [14c]

where:

Q·Q*=I  Equation [15]

based on the orthonormal property of the matrix Q. The matrix Irepresents an identity matrix.

By combining equations [13] and [14c]:

Ĝ=U*·U·S·V*·Q*·V·G+U*·N  Equation [16a]

and

Ĝ=S·V*·Q*·V·G+U*·N  Equation [16b]

where the matrices U and V may also be described as orthonormalmatrices.

When Q is an identity matrix as is the case in conventional MIMOsystems, which transmit sounding frames without beamforming, equation[16b] may be represented:

Ĝ=S·G+U*·N  Equation [16c]

where S is a diagonal matrix as described in equation [12]. If thefeedback matrix V is utilized as a subsequent steering matrix when thematrix Q is not an identity matrix, the first term in equation [16b],S·V*·Q*·V, may not be a diagonal matrix. Thus, in conventional MIMOsystems, the ability to perform channel sounding may depend on thematrix Q being an identity matrix.

Alternatively, the receiving mobile terminal 406 may send the CSI, asrepresented by the matrix H_(eff) in the feedback information. When Q isan identity matrix, as may be the case in conventional MIMO systems, thereceiving mobile terminal may send the matrix H in the feedbackinformation. When the receiving mobile terminal 406 sends the matrix Hin the feedback information, the transmitting mobile terminal 402 maycompute the subsequent steering matrix based on the CSIT.

Various embodiments of the invention may enable channel sounding to beperformed when the matrix Q is not an identity matrix. In variousembodiments of the invention, the receiving mobile terminal 406 maycompute a steering matrix, Q_(Steer), which may be defined as in thefollowing equation:

Q _(Steer) =Q·V  Equation [17]

where the matrix Q may be as defined in equation [4]. The matrix Q mayrepresent a current steering matrix utilized by the transmitting mobileterminal 402 for generating transmitted signal vectors X. The matrixQ_(Steer) may represent a subsequent steering matrix, which may beutilized by the transmitting mobile terminal 402 for generatingsubsequent transmitted signal vectors X. The feedback steering matrix Vmay be represented by an Nss×Nss matrix. The receiving mobile terminal406 may send the feedback steering matrix V, as computed in equation[17], in feedback information to the transmitting mobile terminal 402.The transmitting mobile terminal may utilize the received feedbackinformation, comprising the feedback steering matrix V, in conjunctionwith the current steering matrix Q, to compute the subsequent steeringmatrix Q_(steer). The subsequent steering matrix may be utilized by thetransmitting mobile terminal 402 for generating subsequent transmittedsignal vectors X.

By utilizing the subsequent steering matrix, Q_(Steer), as defined inequation [17], and the channel estimate matrix, H, as defined inequation [14c], in equation [9a]:

Ĝ=U*·H·Q _(Steer) ·G+U*·N  Equation [18a]

and:

Ĝ=U*·U·S·V*·Q*·Q _(Steer) ·G+U*·N  Equation [18b]

and:

Ĝ=U*·U·S·V*·Q*·Q·V·G+U*·N  Equation [18c]

and:

Ĝ=S·V*·V·G+U*·N  Equation [18d]

and:

Ĝ=S·G+U*·N  Equation [18e]

Alternatively, in various embodiments of the invention, the receivingmobile terminal 406 may send the CSI, as represented by the matrixH_(eff) in the feedback information, where H_(eff) may be as defined inequation [10]. When the receiving mobile terminal 406 sends the matrix Hin the feedback information, the transmitting mobile terminal 402 maycompute the subsequent steering matrix, Q_(Steer) as defined in equation[17], based on the CSIT.

In conventional MIMO systems, a receiving mobile terminal 406 may sendfeedback information comprising a subsequent steering matrix V, asrepresented by an Ntx×Nss matrix. In various embodiments of theinvention, a receiving mobile terminal 406 may send feedback informationcomprising a feedback steering matrix V, as represented by an Nss×Nssmatrix. For MIMO systems in which the number of spatial streams is lessthan the number of transmitting antennas, or Nss<Ntx, the quantity offeedback information may be reduced in various embodiments of theinvention in comparison to conventional MIMO systems. This may result ina reduction of overhead transmission for feedback information forvarious embodiments of the invention. This may, in turn, result inhigher information transfer rates for data transmitted between thetransmitting mobile terminal 402 and the receiving mobile terminal 406when compared to conventional MIMO systems.

In addition, in conventional MIMO systems, beamforming may not beutilized by the transmitting mobile terminal 402 when transmittingsounding frames. Thus data may not be transmitted between thetransmitting mobile terminal 402 and the receiving mobile terminal 406when sounding frames are being transmitted. By contrast, in variousembodiments of the invention, beamforming may be utilized whentransmitting sounding frames. This may enable data to be transmittedbetween the transmitting mobile terminal 402 and the receiving mobileterminal 406 while sounding frames are also being transmitted. This mayreduce the amount of time during which data may not be transmittedduring communications between a transmitting mobile terminal 402 and areceiving mobile terminal 406 when compared to conventional MIMOsystems. This may, in turn, result in higher information transfer ratesfor data transmitted between the transmitting mobile terminal 402 andthe receiving mobile terminal 406 when compared to conventional MIMOsystems.

FIG. 5 is an exemplary block diagram of a MIMO transmitter, which may beutilized in connection with an embodiment of the invention. Referring toFIG. 5, there is shown a scrambler 502, an encoder parser 504, aplurality of encoder/puncture blocks 506 a, . . . , and 506 n, a streamparser 508, a plurality of interleaver blocks 510 a, . . . , and 510 n,a plurality of constellation mapper blocks 512 a, . . . , and 512 n, aspace time block coding (STBC) block 514, a cyclical shift diversity(CSD) block 516, a beamforming block 518, a plurality of IFFT blocks 520a, . . . , and 520 n, a plurality of insert guard interval window blocks522 a, . . . , and 522 n, a plurality of radio front end (RFE) blocks524 a, . . . , and 524 n, a plurality of transmitting antennas 526 a, .. . , and 526 n, a processor 532, and a memory 534.

The scrambler 502 may comprise suitable logic, circuitry, and/or codethat may enable scrambling of a pattern of binary 0's and 1's containedwithin transmitted data to prevent long sequences of consecutive 0's or1's. The encoder parser 504 may comprise suitable logic, circuitry,and/or code that may enable receiving bits from a single input stream,and distributing each of the bits to one of a plurality of outputstreams.

The encoder/puncture block 506 a may comprise suitable logic, circuitry,and/or code that may enable received data to be encoded to enable errorcorrection. An encoder/puncture block 506 a may encode data based on aforward error correction (FEC) coding method, such as binaryconvolutional coding (BCC), or low density parity check (LDPC) coding.The encoder/puncture block 506 a may also perform puncturing of encodeddata to modify a coding rate associated with, for example, BCC encoding.The encoder/puncture block 506 n may be substantially similar to theencoder/puncture block 506 a.

The stream parser 508 may comprise suitable logic, circuitry, and/orcode that may receive one or more input data streams, and distributeeach bit from each input data stream to one of a plurality of spatialstreams.

The interleaver 510 a may comprise suitable logic, circuitry, and/orcode that may enable reordering of bits in a received spatial stream.The interleaver 510 a may reorder bits so that if binary values for ablock of contiguous transmitted bits are corrupted during transmission,the block of contiguous transmitted bits may be separated by adeinterleaver. The separation of corrupted bits may enable a FEC codingmethod to be utilized to correct the binary values of bits corruptedduring transmission. The interleaver 510 n may be substantially similarto the interleaver 510 a.

The constellation mapper block 512 a may comprise suitable logic,circuitry, and/or code that may enable a sequence of bits in a receiveddata stream to be mapped to a constellation point. The constellationpoint may be determined based on a modulation type utilized fortransmitting data associated with the spatial stream, for example64-level quadrature amplitude modulation (64-QAM). The constellationpoint may be referred to as a symbol. For example, for 64-QAM, a symbolmay correspond to a binary value for a sequence of 6 bits. Theconstellation mapper block 512 n may be substantially similar to theconstellation mapper block 512 n.

The STBC block 514 may comprise suitable logic, circuitry, and/or codethat may enable reception of symbols from a plurality of input spatialstreams. Each symbol from each spatial stream may be output to at leastone of plurality of space time streams at a given time instant when STBCis utilized by the MIMO transmitter. At a subsequent time instant asymbol from the spatial stream may be output to a different space timestream. In addition to mapping a symbol from a given spatial stream todifferent space time streams at different time instants, the STBC block514 may modify the value of the symbol at different time instants. Forexample, at one time instant, the STBC block 514 may output the value ofthe symbol from a spatial stream on a first space time stream, whileduring a succeeding time instant the STBC block 514 may output a valuethat is a complex conjugate of the symbol, or a negative value of thecomplex conjugate of the symbol, which may be output on a second spacetime stream.

The CSD block 516 may comprise suitable logic, circuitry, and/or codethat may enable input of a stream, and output of a time-shifted versionof the stream. For example, the CSD block 516 may receive an inputstream and output a time-delayed version of the input stream. CSD may beutilized to avoid unintentional beamforming when similar signals aresimultaneously transmitted via a plurality of streams and/or RF chains.

The beamforming block 518 may comprise suitable logic, circuitry, and/orcode that may enable a plurality of RF chains to be generated based onan input plurality of streams. The beamforming block 518 may utilize asteering matrix, where the steering matrix is not an identity matrix.The IFFT blocks 520 a, . . . , and 520 n may be substantially similar tothe IFFT block 410 a.

The insert GI window block 522 a may comprise suitable logic, circuitry,and/or code that may enable insertion of guard intervals in atransmitted RF chain signal. The guard interval may represent a timeinterval between transmission of symbols within the transmitted RF chainsignal. The insert GI window block 522 n may be substantially similar tothe insert GI window block 522 a.

The RFE block 524 a may comprise suitable logic, circuitry, and/or codethat may enable generation of an RF signal from an RF chain signal. TheRFE block 524 a may generate the RF signal by utilizing a plurality offrequency carrier signals to modulate the RF chain signal. The RFE block524 a may be utilized to enable generation of a 20 MHz bandwidth RFsignal, or of a 40 MHz bandwidth RF signal, for example. The modulatedsignal may be transmitted via the transmitting antenna 526 a. The RFEblock 524 n may be substantially similar to the RFE block 524 a. Thetransmitting antenna 526 n may be substantially similar to thetransmitting antenna 526 a.

The processor 532 may comprise suitable logic, circuitry, and/or codethat may enable generation of control signals for the MIMO transmitter.The processor 532 may generate control signals to determinespecifications for FEC coding and/or puncturing that may be performedwithin the MIMO transmitter. The processor 532 may generate controlsignals to determine one or more modulation types to be utilized withinthe MIMO transmitter. The processor 532 may perform computations thatdetermine beamforming coefficients to be utilized in connection withbeamforming of RF streams within the MIMO transmitter. The processor 532may generate data that may be transmitted by the MIMO transmitter. Theprocessor may perform computations on feedback information received by aMIMO receiver 284 (FIG. 2). The memory 534 may be substantially similarto the memory 272.

In operation, the processor 532 may select a coding rate for BCCencoding, for example. The processor 532 may select a different codingrate for each spatial stream. The processor 532 may send control signalsto the encoder/puncture blocks 506 a, . . . , and 506 n to enable FECcoding based on the selected coding rate. The processor 532 may select amodulation type. The processor 532 may select a different modulationtype for each spatial stream. The processor may send control signals tothe constellation mapper blocks 512 a, . . . , and 512 n to enable theselected modulation types. The processor may retrieve data stored inmemory 534 when selecting coding rates, and/or modulation types. Theprocessor 532 may compute a steering matrix based on feedbackinformation and/or stored data in memory 534. The processor 532 mayconfigure the beamforming block 518 based on coefficients in thecomputed steering matrix.

The processor 532 may generate data to be transmitted by the MIMOtransmitter. The data may be communicated in a binary input stream tothe scrambler block 502. The scrambler block 502 may scramble the datautilizing a scrambling polynomial and output the scrambled bits to theencoder parser block 504. The encoder parser block 504 may distributethe scrambled bits among the encoder/puncture blocks 506 a, . . . , and506 n. The encoder parser block 504 may distribute the scrambled bits ina round robin fashion, for example. Each encoder parser block 504 mayutilize a corresponding selected FEC coding method for encoding receivedbits. The plurality of encoder/puncture blocks 506 a, . . . , and 506 nmay be output to the stream parser 508, which may distribute the encodedbits among a plurality of Nss spatial streams, for example. Each of theinterleavers 510 a, . . . , and 510 n may perform bit interleaving onthe bits within the corresponding spatial stream. Each of theconstellation mapper blocks 512 a, . . . , and 512 n may utilize acorresponding selected modulation type to generate symbols for bitsreceived in each spatial stream.

If STBC is utilized by the MIMO transmitter, the STBC block 514 maygenerate a plurality of Nsts space time streams based on the Nss spatialstreams received from the plurality of constellation mapper blocks 512a, . . . , and 512 n. If CSD is utilized by the MIMO transmitter, theCSD block 516 may generate time shifted versions of one or more spatialstreams or space time streams. The CSD block 516 may insert a time shiftfor one stream based on another stream. For example, a first stream notmay be time shifted, while a second stream may be time delayed by 200 nsrelative to the first stream.

The beamforming block 518 may generate a plurality of RF chain signalsbased on a plurality of received spatial streams and/or space timestreams. Each of the plurality of IFFT blocks 520 a, . . . , and 520 nmay generate a time-domain representation for one of the RF chainsignals. Each of the plurality of insert GI window blocks 522 a, . . . ,and 522 n may insert a GI between symbols transmitted via one of the RFchain signals. Each of the plurality of RFE blocks 524 a, . . . , and524 n may generate an RF signal for one of the RF chain signals. Each ofthe plurality of antennas 526 a, . . . , and 526 n may be utilized fortransmitting one of the generated RF signals via a wirelesscommunications medium 404.

In various embodiments of the invention, the processor 532 may configurethe MIMO transmitter to transmit a sounding frame in a physical (PHY)layer protocol data unit (PDU) while simultaneously sending data in amedium access control layer PDU contained in a service data unit (SDU)segment of the PHY PDU. The PHY PDU may be transmitted utilizingbeamforming at the beamforming block 518.

FIG. 6 is a diagram that illustrates exemplary frame exchange in aconventional channel sounding procedure, which may be utilized inconnection with an embodiment of the invention. Referring to FIG. 6,there is shown a plurality of frames sent by a MIMO transmitter, forexample an AP 108 (FIG. 1), and by a MIMO receiver, for example an802.11 WLAN station 104. In frame 602, the MIMO transmitter 108 maytransmit data via transmitted RF chains utilizing beamforming. Thebeamforming may utilize a current steering matrix Q_(Current). At theend of transmission of the frame 602, a feedback time interval, theduration of which is indicated as T_(Feedback) in FIG. 6, may begin. Thetime interval, T_(Feedback), may measure the amount of time utilized forperforming a channel sounding procedure.

At the beginning of the feedback time interval, a backoff time duration,which is indicated as T_(Backoff) in FIG. 6, may elapse. The backofftime duration may specify a period of time that may elapse before theMIMO transmitter 108 may attempt to transmit a subsequent frame via thewireless communications medium 404. At the end of the backoff timeduration, in frame 604, the MIMO transmitter 108 may transmit a soundingframe. The sounding frame may comprise a request to the recipient MIMOreceiver 104 to generate channel state information to measure thedownlink RF channel from the MIMO transmitter 108 to the MIMO receiver104, H_(Down) (FIG. 3). The sounding frame 604 may be transmittedwithout utilizing beamforming, or Q=I, where I is an identity matrix.

At the end of transmission of the sounding frame 604, a short interframespacing (SIFS) time interval, the duration of which is indicated asT_(SIFS) in FIG. 6, may begin. The SIFS time interval may specify a timeduration that may elapse before the MIMO receiver 104 may transmit aframe in response to the sounding frame 604. At the end of the SIFS timeinterval, the MIMO receiver 104 may transmit a clear to send (CTS)response frame 606. The response frame 606 may comprise channel stateinformation and/or a steering matrix, V, computed by the MIMO receiver104, based on the CSI. In a response frame 606 that comprises a steeringmatrix V, the matrix V may be a 4×2 matrix when the number oftransmitting antenna Ntx=4 at the MIMO transmitter 108, the number ofspatial streams Nss=2, and the number of receiving antennas Nrx=2 at theMIMO receiver 104. The response frame 606 may be transmitted by the MIMOreceiver 104 without utilizing beamforming.

At the end of transmission of the response frame 606, another SIFS timeinterval may begin. The SIFS time interval may specify a time durationthat may elapse before the MIMO transmitter 108 may transmit a framesubsequent to receipt of the response frame 606 from the MIMOtransmitter 104. At the end of the SIFS time interval, the MIMOtransmitter 108 may transmit a data frame 608 comprising data from a MACPDU. The data frame 608 may be transmitted via transmitted RF chainsutilizing beamforming. The beamforming may be performed based on thesteering matrix V received in the response frame 606, or based on asteering matrix V that was computed based on CSI contained in theresponse frame 606. The data frame 608 may also comprise PHY layer data,for example, the data frame 608 may comprise a request that the MIMOreceiver 104 respond with information that may be utilized by the MIMOtransmitter 108 for selecting one or more modulation types, and/or oneor more coding rate that may be utilized in connection with acorresponding one or more spatial streams transmitted by the MIMOtransmitter 108.

At the end of transmission of the data frame 608, another SIFS timeinterval may begin. The SIFS time interval may specify a time durationthat may elapse before the MIMO receiver 104 may transmit a framesubsequent to receipt of the data frame 608 from the MIMO transmitter108. At the end of the SIFS time interval, the MIMO receiver 104 maytransmit an acknowledgement frame 610 to the MIMO transmitter 108. Theacknowledgement frame 610 may acknowledge receipt of the data containedwithin the data frame 608, and may comprise modulation type and/orcoding rate information. The acknowledgement frame 610 may also compriseCSI. The end of transmission of the acknowledgement frame 610 maycorrespond to the end of the channel sounding procedure.

FIG. 7 is a diagram that illustrates exemplary frame exchange utilizinga non-identity steering matrix in a channel sounding procedure, inaccordance with an embodiment of the invention. Referring to FIG. 7,there is shown a plurality of frames sent by a MIMO transmitter, forexample an AP 108 (FIG. 1), and by a MIMO receiver, for example an802.11 WLAN station 104. In frame 702, the MIMO transmitter 108 maytransmit data via transmitted RF chains utilizing beamforming. Thebeamforming may utilize a current steering matrix Q_(Current). At theend of transmission of the frame 702, a feedback time interval, theduration of which is indicated as T_(Feedback) in FIG. 7, may begin. Thetime interval, T_(Feedback), may measure they amount of time utilizedfor performing a channel sounding procedure.

At the beginning of the feedback time interval, a backoff time duration,which is indicated as T_(Backoff) in FIG. 7, may elapse. The backofftime duration may specify a period of time that may elapse before theMIMO transmitter 108 may attempt to transmit a subsequent frame via thewireless communications medium 404. At the end of the backoff timeduration, in frame 704, the MIMO transmitter 108 may transmit a soundingframe. The sounding frame may comprise a request to the recipient MIMOreceiver 104 to generate channel state information to measure thedownlink RF channel from the MIMO transmitter 108 to the MIMO receiver104, H_(Down) (FIG. 3). The sounding frame 704 may be transmitted whileutilizing a generalized steering matrix Q_(Gen), or Q=Q_(Gen), whereQ_(Gen) is not an identity matrix.

At the end of transmission of the sounding frame 704, a short interframespacing (SIFS) time interval, the duration of which is indicated asT_(SIFS) in FIG. 7, may begin. The SIFS time interval may specify a timeduration that may elapse before the MIMO receiver 104 may transmit aframe in response to the sounding frame 704. At the end of the SIFS timeinterval, the MIMO receiver 104 may transmit a clear to send (CTS)response frame 706. The response frame 706 may comprise channel stateinformation and/or a feedback steering matrix, V, computed by the MIMOreceiver 104, based on the CSI, and based on a non-identity steeringmatrix Q_(Gen). The feedback steering matrix V may be computed by theMIMO receiver 104 as described for equations [17], and [18a-e]. In aresponse frame 706 that comprises a feedback steering matrix V, thefeedback steering matrix V may be a 2×2 matrix when the number oftransmitting antenna Ntx=4 at the MIMO transmitter 108, the number ofspatial streams Nss=2, and the number of receiving antennas Nrx=2 at theMIMO receiver 104. The response frame 706 may be transmitted by the MIMOreceiver 104 without utilizing beamforming. The quantity of feedbackinformation contained in the response frame 706 may be about ¼ of thequantity of feedback information contained in the response frame 606 asshown in Tables 1 and 2 below.

At the end of transmission of the response frame 706, another SIFS timeinterval may begin. The SIFS time interval may specify a time durationthat may elapse before the MIMO transmitter 108 may transmit a framesubsequent to receipt of the response frame 706 from the MIMOtransmitter 104. At the end of the SIFS time interval, the MIMOtransmitter 108 may transmit a data frame 708 comprising data from a MACPDU. The data frame 708 may be transmitted via transmitted RF chainsutilizing beamforming. The beamforming may be performed based on thefeedback steering matrix V computed based on the matrix productQ_(Gen)·V, where V may represent the feedback steering matrix receivedin the response frame 706. The data frame 708 may also comprise PHYlayer data, for example, the data frame 708 may comprise a request thatthe MIMO receiver 104 respond with information that may be utilized bythe MIMO transmitter 108 for selecting one or more modulation types,and/or one or more coding rate that may be utilized in connection with acorresponding one or more spatial streams transmitted by the MIMOtransmitter 108.

At the end of transmission of the data frame 708, another SIFS timeinterval may begin. The SIFS time interval may specify a time durationthat may elapse before the MIMO receiver 104 may transmit a framesubsequent to receipt of the data frame 708 from the MIMO transmitter108. At the end of the SIFS time interval, the MIMO receiver 104 maytransmit an acknowledgement frame 710 to the MIMO transmitter 108. Theacknowledgement frame 710 may acknowledge receipt of the data containedwithin the data frame 708, and may comprise modulation type and/orcoding rate information. The acknowledgement frame 710 may also compriseCSI. The end of transmission of the acknowledgement frame 710 maycorrespond to the end of the channel sounding procedure.

FIG. 8 is a diagram that illustrates exemplary frame exchange fortransmitting data within channel sounding frames, in accordance with anembodiment of the invention. Referring to FIG. 8, there is shown aplurality of frames sent by a MIMO transmitter, for example an AP 108(FIG. 1), and by a MIMO receiver, for example an 802.11 WLAN station104. The time interval T_(Feedback), which is indicated in FIG. 8, maymeasure they amount of time utilized for performing a channel soundingprocedure.

At the beginning of the feedback time interval, a backoff time duration,which is indicated as T_(Backoff) in FIG. 8, may elapse. The backofftime duration may specify a period of time that may elapse before theMIMO transmitter 108 may attempt to transmit a frame via the wirelesscommunications medium 404 to initiate the channel sounding procedure. Atthe end of the backoff time duration, in frame 802, the MIMO transmitter108 may transmit a sounding frame. The sounding frame may comprise arequest to the recipient MIMO receiver 104 to generate channel stateinformation to measure the downlink RF channel from the MIMO transmitter108 to the MIMO receiver 104, H_(Down) (FIG. 3). The sounding frame 802may also comprise data. The sounding frame 802 may be transmitted whileutilizing a current steering matrix Q_(Current), or Q=Q_(Current), whereQ_(Current) is not an identity matrix. The current steering matrix,Q_(Current), may be a steering matrix that is currently being utilizedby the MIMO transmitter 108 to transmit data frames via the wirelesscommunications medium 404.

At the end of transmission of the sounding frame 802, a short interframespacing (SIFS) time interval, the duration of which is indicated asT_(SIFS) in FIG. 8, may begin. The SIFS time interval may specify a timeduration that may elapse before the MIMO receiver 104 may transmit aframe in response to the sounding frame 802. At the end of the SIFS timeinterval, the MIMO receiver 104 may transmit an acknowledgement frame804. The acknowledgement frame 804 may also comprise channel stateinformation and/or a feedback steering matrix, V, computed by the MIMOreceiver 104, based on the CSI, and based on a non-identity steeringmatrix Q_(Current). The feedback steering matrix V may be computed bythe MIMO receiver 104 as described for equations [17], and [18 a-e]. Inan acknowledgement frame 804 that comprises a feedback steering matrixV, the feedback steering matrix V may be a 2×2 matrix when the number oftransmitting antenna Ntx=4 at the MIMO transmitter 108, the number ofspatial streams Nss=2, and the number of receiving antennas Nrx=2 at theMIMO receiver 104. The acknowledgement frame 804 may be transmitted bythe MIMO receiver 104 without utilizing beamforming. The quantity offeedback information contained in the acknowledgement frame 804 may beabout ¼ of the quantity of feedback information contained in theresponse frame 606 as shown in Tables 1 and 2 below. The end oftransmission of the acknowledgement frame 804 may correspond to the endof the channel sounding procedure. Following another backoff timeduration, the MIMO transmitter 108 may transmit data frames 806utilizing a steering matrix computed based on the matrix productQ_(Current)·V.

In various embodiments of the invention, the amount of time utilized inperforming the channel sounding procedure of FIG. 8 may be less incomparison to the amount of time utilized in conventional channelsounding methods, such as is illustrated in FIG. 6.

Table 1 presents exemplary comparisons between the number of bytescontained in feedback information for different feedback arraydimensions, which may be utilized in connection with an embodiment ofthe invention. The comparison in Table 1 may be based on a 20 MHz type ERF channel as specified in IEEE 802.11. The first row in Table 1represents a number of bytes contained in feedback information, which isgenerated based on a Cartesian coordinate format representation. Thesecond row in Table 1 represents a number of bytes contained in feedbackinformation, which is generated based on Givens rotations withoututilizing tone grouping. Tone grouping may not be utilized when a tonegroup size ε=1, for example. The third row in Table 1 represents anumber of bytes contained in feedback information, which is generatedbased on Givens rotations utilizing a tone group size ε=2. The fourthrow in Table 1 represents a number of bytes contained in feedbackinformation, which is generated based on Givens rotations utilizing atone group size ε=4. The first column in Table 1 represents a size of aV matrix where N=2 and M=2, where N is a variable representing thenumber of rows, and M is a variable representing the number of columns.The second column in Table 1 represents a size of a V matrix where N=3and M=3. The third column in Table 1 represents a size of a V matrixwhere N=4 and M=2. The fourth column in Table 1 represents a size of a Vmatrix where N=4 and M=4.

When the tone group size is 4, a V matrix that may be represented as a2×2 matrix may comprise about 14 bytes of binary data. By comparison, aV matrix that may be represented as a 4×2 matrix may comprise about 53bytes of binary data. Similarly, when the tone group size is 2, a Vmatrix that may be represented as a 2×2 matrix may comprise about 28bytes of binary data. By comparison, a V matrix that may be representedas a 4×2 matrix may comprise about 105 bytes of binary data.

TABLE 1 Quantity of Feedback Information for 20 MHz Type E Channel(Bytes) 2 × 2 3 × 3 4 × 2 4 × 4 Cartesian 280 504 448 896 Givens 56 168210 336 (252) Tone Group Size = 2 28 84 105 168 (126) Tone Group Size =4 14 42 53  84 (63)

Table 2 presents exemplary comparisons between the numbers of bytescontained in feedback information for various feedback array dimensions,which may be utilized in connection with an embodiment of the invention.Table 2 represents equivalent information from Table 1 where the RFchannel is 40 MHz. The comparison in Table 2 may be based on a 40 MHztype E RF channel as specified in IEEE 802.11. The first row in Table 2represents a number of bytes contained in feedback information, which isgenerated based on a Cartesian coordinate format representation. Thesecond row in Table 2 represents a number of bytes contained in feedbackinformation, which is generated based on Givens rotations withoututilizing tone grouping. The third row in Table 2 represents a number ofbytes contained in feedback information, which is generated based onGivens rotations utilizing a tone group size ε=2. The fourth row inTable 2 represents a number of bytes contained in feedback information,which is generated based on Givens rotations utilizing a tone group sizeε=4.

The first column in Table 2 represents a size of a V matrix where N=2and M=2. The second column in Table 2 represents a size of a V matrixwhere N=3 and M=3. The third column in Table 2 represents a size of a Vmatrix where N=4 and M=2. The fourth column in Table 2 represents a sizeof a V matrix where N=4 and M=4.

When the tone group size is 4, a V matrix that may be represented as a2×2 matrix may comprise about 28 bytes of binary data. By comparison, aV matrix that may be represented as a 4×2 matrix may comprise about 105bytes of binary data. Similarly, when the tone group size is 2, a Vmatrix that may be represented as a 2×2 matrix may comprise about 56bytes of binary data. By comparison, a V matrix that may be representedas a 4×2 matrix may comprise about 210 bytes of binary data.

TABLE 2 Quantity of Feedback Information for 40 MHz Type E Channel(Bytes) 2 × 2 3 × 3 4 × 2 4 × 4 Cartesian 570 1,026 912 1,824 Givens 114342 428 684 (513) Tone Group Size = 2 56 168 210 336 (252) Tone GroupSize = 4 28 84 105 168 (126)

FIG. 9 is a diagram illustrating an exemplary signal header field, whichmay be utilized in connection with an embodiment of the invention. Thesignal (SIG) header field is a field within a PHY PDU that identifiesthe PDU and may be utilized to communicate PHY layer configurationinformation that is utilized by the MIMO transmitter described in FIG.5. The signal header field may also be utilized by a MIMO receiver 104to identify a received sounding frame.

Referring to FIG. 9, there is shown a SIG header field 902. The SIGheader field 902 may comprise a modulation and coding scheme (MCS) field904, a 20 MHz/40 MHz bandwidth indication 906, a length field 908, asmoothing indication 910, a not sounding indication 912, a reservedfield 914, an aggregation indication 916, an STBC indication 918, anadvanced coding indication 920, a short GI indication 922, a number ofhigh throughput long training fields utilized indication 924, a cyclicalredundancy check field, 926, and a tail field 928.

The MCS field 904 may comprise 7 bits of binary information. The MCSfield 904 may indicate the modulation type and coding rate beingutilized in the coding of a PHY PDU (PPDU). The 20 MHz/40 MHz bandwidthfield 906 may comprise 1 bit of binary information. The 20 MHz/40 MHzbandwidth field 906 may indicate whether the PPDU is to be transmittedutilizing a 20 MHz RF channel, or a 40 MHz RF channel. The length field908 may comprise 16 bits of binary information. The length field 908 mayindicate the number of octets of binary information that is contained inthe physical layer service data unit (PSDU) field within a PPDU. ThePSDU may comprise a MAC PDU, for example. The smoothing indication 910may comprise 1 bit of binary information. The smoothing indication 910may indicate whether channel estimation may be performed in connectionwith tone grouping. If smoothing enabled, a channel estimate matrix Hmay be computed based on a measured portion of the frequency carriersassociated with the corresponding RF channel, where estimates for theremaining frequency carriers may be computed based on the measuredfrequency carriers.

The not sounding indication 912 may comprise 1 bit of binaryinformation. The not sounding indication 912 may indicate whether thePPDU is a sounding frame. The not sounding indication may comprise abinary value 0 to indicate that the PPDU is a sounding frame. Thereserved field 914 may comprise 1 bit of binary information. Thereserved field 914 may comprise no assigned utilization. The aggregationfield 916 may comprise 1 bit of binary information. The aggregationfield 916 may indicate whether the PSDU within the PPDU comprises datathat is to be aggregated with a data contained in a PSDU in a subsequentPPDU. The STBC indication 918 may comprise 2 bits of binary information.The STBC indication 918 may indicate a difference between the number ofspatial streams Nss, and the number of space time streams, Nsts. WhenNss=Nsts is indicated, STBC may not be utilized by the MIMO transmitter.The advanced coding field 920 may comprise 1 bit of binary information.The advanced coding field 920 may indicate whether binary convolutionalcoding (BCC), or low density parity check (LDPC) coding is utilized inthe coding of PPDUs at the MIMO transmitter.

The short GI field 488 may comprise 1 bit of binary information. Theshort GI field 922 may indicate the length, as measured in ns forexample, of the guard interval utilized when transmitting symbols inPPDUs transmitted via an RF chain. The number of HT-LTF field 924 maycomprise 2 bits of binary information. The number of HT-LTF field 924may indicate the number of high throughput long training fieldscontained in a transmitted PPDU. The long training fields may beutilized by a MIMO receiver when computing a channel estimate matrix H.The CRC field 926 may comprise 8 bits of binary information. The CRCfield 926 may be computed by a MIMO transmitter, and utilized by a MIMOreceiver for detecting and/or correcting errors in a received PPDU. Thetail field 928 may comprise 6 bits of binary information. The tail field928 may be utilized to extend the number of binary bits contained in anSIG field to a desired length, for example to an integer multiple of 8bits.

FIG. 10 is a flowchart illustrating exemplary steps for exemplary frameexchange for transmitting data within channel sounding frames, inaccordance with an embodiment of the invention. Referring to FIG. 10, instep 1002, a MIMO transmitter 108 may transmit data within a soundingPPDU utilizing beamforming based on a current steering matrixQ_(Current). In step 1004, the MIMO transmitter 108 may receive feedbackinformation from the MIMO receiver 104. Step 1006 may determine whetherthe feedback information comprises CSI or a feedback steering matrix. Ifstep 1006 determines that the feedback information comprises CSI, instep 1008, the MIMO transmitter 108 may compute a subsequent steeringmatrix Q_(Current)·V based on the CSI, as represented by a channelestimate matrix H_(Eff). In step 1012, the MIMO transmitter 108 maytransmit subsequent data utilizing beamforming based on the subsequentsteering matrix Q_(Current)·V.

If step 1006 determines that the feedback information comprises afeedback steering matrix, in step 1010, the MIMO transmitter 108 mayreceive the feedback steering matrix V from the feedback information.The feedback steering matrix may be utilized by the MIMO transmitter 108to compute the subsequent steering matrix Q_(Current)·V. Step 1012 mayfollow step 1010.

FIG. 11 is a flowchart illustrating exemplary steps for exemplary frameexchange for transmitting channel sounding frames utilizing anon-identity steering matrix, in accordance with an embodiment of theinvention. Referring to FIG. 11, in step 1102, a MIMO transmitter 108may transmit data frames utilizing beamforming based on a currentsteering matrix Q_(Current). In step 1104, the MIMO transmitter 108 maytransmit a sounding frame utilizing a steering matrix, Q_(Gen), wherethe matrix Q_(Gen) is not an identity matrix. In step 1106, the MIMOtransmitter 108 may receive feedback information from the MIMO receiver104. Step 1108 may determine whether the feedback information comprisesCSI or a feedback steering matrix. If step 1108 determines that thefeedback information comprises CSI, in step 1110, the MIMO transmitter108 may compute a subsequent steering matrix Q_(Current)·V based on theCSI, as represented by a channel estimate matrix H_(Eff). In step 1114,the MIMO transmitter 108 may transmit a frame comprising data an amodulation type and coding rate request. The frame may be transmittedutilizing beamforming based on the subsequent steering matrixQ_(Current)·V. In step 1116, the MIMO transmitter 108 may receive anacknowledgement frame from the MIMO receiver 104. The acknowledgementframe may comprise one or more suggested modulation types,Mod_(Feedback), and/or one or more suggested coding ratesFEC_(Feedback). In step 1118, the MIMO transmitter 108 may transmitsubsequent data frames utilizing a steering matrix, one or moremodulation types, and/or one or more coding rates, based on feedbackinformation received during the channel sounding procedure.

If step 1108 determines that the feedback information comprises afeedback steering matrix, in step 1112, the MIMO transmitter 108 mayreceive the feedback steering matrix V from the feedback information.The feedback steering matrix may be utilized by the MIMO transmitter 108to compute the subsequent steering matrix Q_(Current)·V. Step 1114 mayfollow step 1112.

Aspects of a system for explicit feedback with sounding packets forwireless local area networks may comprise a beamforming block 518 thatmay enable generation of a plurality of RF chain signals based on acurrent steering matrix, where the current steering matrix may be anon-identity matrix. A processor 532 may enable transmission of arequest for feedback information via the plurality of RF chain signals.The request may comprise medium access control (MAC) layer protocol dataunit (PDU) data and channel sounding information, which may beencapsulated in a physical (PHY) layer PDU. A receiver 284 may enablereception of the feedback information.

The processor 532 may enable computation of a subsequent steering matrixbased on the received feedback information. The beamforming block 518may enable transmission of subsequent MAC layer PDU data based on thesubsequent steering matrix. The received feedback information maycomprise a channel estimate matrix and/or a feedback steering matrix.The subsequent steering matrix may be the feedback steering matrix. Theprocessor 532 may enable computation of the subsequent steering matrixfrom the channel estimate matrix by a singular value decomposition (SVD)method. The feedback steering matrix may be represented as an Nss×Nssmatrix, where Nss may be a variable representing a number of spatialstreams transmitted via the plurality of RF chain signals.

In another aspect of the system the processor 532 may enabletransmission of a request for modulation type information and/or codingtype information via a subsequent plurality of RF chain signalsgenerated based on the subsequent steering matrix. The request maycomprise medium access control (MAC) layer protocol data unit (PDU) dataand a modulation and coding request, which may be encapsulated in aphysical (PHY) layer PDU. A receiver 284 may enable reception of anacknowledgement PHY PDU comprising the modulation type informationand/or coding type information. The processor 532 may enabletransmission of subsequent data based on the received acknowledgementPHY PDU.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method for communicating information in awireless communication system comprising: generating a plurality ofradio frequency (RF) chain signals based on a current steering matrix,wherein the current steering matrix is a non-identity matrix; andtransmitting a request for feedback information via the plurality of RFchain signals, the request comprising medium access control (MAC) layerprotocol data unit (PDU) data and channel sounding information.
 2. Themethod of claim 1, wherein the MAC layer PDU data and the channelsounding information are encapsulated in a single physical (PHY) layerPDU.
 3. The method of claim 1, wherein the MAC layer PDU data and thechannel sounding information are encapsulated in differing physical(PHY) layer PDUs
 4. The method of claim 1, further comprising receivingfeedback information in response to the request.
 5. The method of 4,further comprising computing a subsequent steering matrix based on thereceived feedback information.
 6. The method of claim 5, furthercomprising transmitting subsequent MAC layer PDU data based on thesubsequent steering matrix.
 7. The method of claim 4, wherein thereceived feedback information comprises at least one of: a channelestimate matrix, and a feedback steering matrix when computing thesubsequent steering matrix.
 8. A wireless device comprising: a wirelesstransmitter; a wireless receiver; and processing circuitry, the wirelesstransmitter, wireless receiver, and processing circuitry configured to:generate a plurality of radio frequency (RF) chain signals based on acurrent steering matrix, wherein the current steering matrix is anon-identity matrix; and transmit a request for feedback information viathe plurality of RF chain signals, the request comprising medium accesscontrol (MAC) layer protocol data unit (PDU) data and channel soundinginformation.
 9. The wireless device of claim 8, wherein the MAC layerPDU data and the channel sounding information are encapsulated in asingle physical (PHY) layer PDU.
 10. The wireless device of claim 8,wherein the MAC layer PDU data and the channel sounding information areencapsulated in differing physical (PHY) layer PDUs
 11. The wirelessdevice of claim 8, wherein the wireless transmitter, wireless receiver,and processing circuitry are further configured to receive feedbackinformation in response to the request.
 12. The wireless device of 11,wherein the processing circuitry is further configured to compute asubsequent steering matrix based on the received feedback information.13. The wireless device of claim 12, wherein the wireless transmitter,wireless receiver, and processing circuitry are further configured totransmit subsequent MAC layer PDU data based on the subsequent steeringmatrix.
 14. The wireless device of claim 11, wherein the receivedfeedback information comprises at least one of: a channel estimatematrix, and a feedback steering matrix when computing the subsequentsteering matrix.
 15. The wireless device of claim 8, wherein thewireless transmitter and wireless receiver support Wireless Local AreaNetwork (WLAN) communications.
 16. A method for communicatinginformation in a wireless communication system comprising: generating aplurality of radio frequency (RF) chain signals based on a currentsteering matrix, wherein the current steering matrix is a non-identitymatrix; and transmitting a request for feedback information via theplurality of RF chain signals, the request comprising medium accesscontrol (MAC) layer protocol data unit (PDU) data in a first physical(PHY) layer PDU and channel sounding information in a PHY layer PDU. 17.The method of claim 16, further comprising receiving feedbackinformation in response to the request.
 18. The method of 17, furthercomprising computing a subsequent steering matrix based on the receivedfeedback information.
 19. The method of claim 18, further comprisingtransmitting subsequent MAC layer PDU data based on the subsequentsteering matrix.
 20. The method of claim 17, wherein the receivedfeedback information comprises at least one of: a channel estimatematrix, and a feedback steering matrix when computing the subsequentsteering matrix.